Technical Principals of Liquids & Misc. Collection and Extraction Methods
PRINCIPAL: What is "Displacement"; and how does it work?
Archimedes discovered that any floating object displaces its own weight of fluid. Something placed within something must "displace" the
molecules equal to itself. How else would it fit? The same principal applies to water flowing into a closed system occupied by air (it's not a vacuum). Where water goes in,
an equal amount of air must go out. This is why most rain barrel systems must have a way of venting their air. Some methods of collecting rainwater have the air and
water exchange in the same tube. When enough water enters, it creates pressure. This internal pressure forces air out (essentially 'clogging' the intake tube temporarily to let out air). The greater
physical weight of the water 'falling' is enough to force its way past the air coming back out. Otherwise, the barrel would not fill.
It's the same principal when you see air bubbles enter a water cooler as you are filling your cup, but in this example air is displacing water.
PRINCIPAL: So who is this guy Pascal, and why does water seek its own level; what does that even mean?
Blaise Pascal (b. 1623) was a French mathematician "of the first order". He built mechanical calculators and introduced new areas of mathematics research.
His main contributions, as far as we're concerned, is his work in hydrodynamics and hydrostatics (centered on the principles of hydraulic fluids). In fact he invented the hydraulic press and the
syringe. Fantastic! In the physical sciences, Pascal's law (the principle of transmission of fluid-pressure) states that "pressure exerted anywhere in a confined incompressible fluid is
transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same."
(Bloomfield, Louis (2006). How Things Work: The Physics of Everyday Life (Third Edition).)
Basically, he discovered two things that explain water seeking its own level, the first was that
pressure on a liquid is transferred through the liquid equally in all directions (regardless of the amount of liquid present). The second was that pressure experienced by a liquid changed at different heights
(barometric, atmospheric, or air-pressure), meaning that liquid which was physically higher in space had a different amount of pressure applied to it. Because of this principal, atmospheric pressure upon liquid in a
confined and connected system will seek to equalize its level. And the weirdest part is that the physical amount or proportions of liquid in the equalizing containers doesn't matter.
It will ALWAYS level out to exactly the same height from the ground.
Many people have this question and hold an intuitive belief that gravity will create a significant amount of water pressure (weight) at the bottom
of the barrel and in turn force the water out a spigot and hose with considerable force. We admit, it would be fantastic if this were the case. However, for as heavy as water is, the only force
with consequence is the force of air (barometric pressure) pushing down on the water. The water will essentially 'fall' out of the barrel, but with only the force of falling water. It will flow
so long as it is falling (flowing downward). It will not fall with any pressure behind it, and if you are holding a hose higher than the top-most level of the water, it will not flow at all.
Otherwise it will spill out with hardly any force whatever. This is sometimes desirable for those who wish to
drip-irrigate with their rainwater.
PRINCIPAL: What is "wicking"? How can water move upwards against gravity?
Wicking is scientifically explained using a physics principal called capillary action.
"Capillary action occurs because of inter-molecular attractive forces between the liquid and solid surrounding surfaces.
If the diameter of [a] tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid)
and forces of adhesion between the liquid and container act to lift the liquid." (http://science.jrank.org/pages/1182/Capillary-Action.html)
Basically, we've all seen a meniscus in our drinking glass. Water has a magical property of "crawing" up surfaces that are unlike itself.
Wicking is (more or less) a plethora of crawling meniscus, but each moment the meniscus encounters another particle to crawl up, hence the
water soaks into certain material, even vertically. In our case, we are using soil wicks to absorb the water.
ALT. METHOD: I want an extraction method that has good water pressure. What about pressurizing the barrels?
We have had a few folks who bought barrels from us with the intention of pressurizing them. To us, it doesn't make sense to pressurize the system at
its most dangerous point; i.e. creating a potential explosion where all the water is stored. Most systems we have seen pick another point at which to introduce 'pressure'. It takes energy to
create pressure, and a COMPLETELY sealed and sound system to maintain pressure (not even tires can always maintain their pressure). Why not use the energy on demand to create water pressure
when you need it, like in a pump extraction method? Or if you must create and maintain pressure in the system, most we've seen use
an air compressor attached to the system. In short, we do not recommend unnecessarily pressurizing the water barrels themselves.
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